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Dynamic spinal stabilization device

Dynamic spinal stabilization device description/claims

This application is a continuation-in part of pending utility application Ser. No. 11/728,204, filed Mar. 23, 2007, entitled DYNAMIC SPINAL STABILIZATION DEVICE, which Application is related to and claims priority to U.S. Provisional Patent Application Ser. No. 60/847,069, filed Sep. 25, 2006, entitled PROSTHETIC FACET JOINT COMPONENT, and U.S. Provisional Patent Application Ser. No. 60/811,843, filed Jun. 8, 2006, entitled PROSTHETIC FACET JOINT, the entirety of each of which is incorporated herein by reference.

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The present invention relates generally to spinal prostheses, and more particularly, towards a method and system for stabilization of a spinal segment.

A significant portion of the population has experiences pain or discomfort resulting from spinal injuries or degenerative conditions in and around the vertebral discs. While many individuals may simply experience minor sprains or strains that may be somewhat limiting, numerous individuals may develop severe lower back pain caused by inflammatory changes in the lumbar disc associated with such changes.

A spinal segment includes a lumbar disc and two facet joints. Degenerative changes in the disc can lead to changes in the facet joint, and vice versa. In order to treat a degenerative condition and to alleviate the pain involved with such a malady, surgical methods may be employed to replace the degenerative component of the spinal segment, such as the damaged disc. However, the replacement of a degenerative disc may not suffice, as the facet joint components of the spinal column may still be a source of discomfort and/or limited mobility. As such, it may desirable to replace a degenerative or problematic facet joint with a posterior stabilization device.

In addition, the degenerative process may result in a condition called spinal stenosis, where there is a narrowing of the spinal canal. This is caused by a combination of reduced disc height, ligamnetum hypertrophy, a forward slip of the vertebra and disc bulging. Surgery is sometime needed to deal with this condition, where a surgical procedure may involve decompression of the spine and/or the removal of posterior portions of the spinal column. This often makes the spine unstable, requiring stabilization of the spine after the decompression. Such stabilization may be achieved with an instrumented postero-lateral fusion, where pedicle screws are inserted into the vertebra to be fused and connected with rods or plates, and bone is laid on the side of the spine over the transverse processes. Stabilization may also be accomplished by a dynamic stabilization device where there is no need to add a fusion, and the device stabilizes the spine. A posterior dynamic stabilization device is typically attached to pedicle screws inserted in to the vertebrae, however, conventional devices are limited in their allowable range of motion and results may vary from patient to patient. It would be desirable to allow the surgeon to select or otherwise adjust the amount of motion desired in the stabilization device based on the requirements of the individual patient.

However, each motion segment of the spine moves around an instantaneous center of rotation. The instantaneous axis of rotation is the axis perpendicular to the plane of motion passing through a point in the body that does not move. For each spinal motion segment this point is basically the point at which the motion segment rotates about, also termed the center of rotation. If the spine is altered in any way, such as with disc and facet degeneration or spinal implantation, this center of rotation shifts, leading to undesirable consequences, such as further degradation, limited movement ability, etc.

Accordingly, it would be desirable to provide a stabilization device which results in a minimum reduction in the natural movement of a motion segment of the spinal column when implanted, thereby reducing any additional strain on the adjacent level of the spinal segment of the individual receiving the stabilization device. Moreover, it would be desirable to provide a stabilization device able to resist and/or dampen the flexion and extension forces experienced by the motion segment during movement, while providing limited motion in the desired directions. It would also be desirable to provide a stabilization device having an adjustable path of motion that can be selectively adjusted for a particular patient or application. In addition, it would further be desirable to provide a stabilization device which can continuously adjust to a moving centre of rotation of a disc prosthesis, or, if used on its own, with that of the lumbar disc anteriorly.

The present invention provides a dynamic stabilization device providing a minimum reduction in the natural movement of the motion segment and reducing any additional strain on the adjacent level of the spinal column in the individual receiving the stabilization device. Moreover, the present invention provides a dynamic stabilization device able to also resist and/or dampen the flexion and extension forces experienced by the motion segment during movement. The dynamic stabilization device may further provide an arcuate or angular path of movement that closely approximates the arc of motion of a healthy lumbar segment, while also having a selectively adjustable path of motion for a particular application or patient. Furthermore, the present invention provides a dynamic stabilization device which can continuously adjust to a moving centre of rotation of an intervertebral disc prosthesis, or that of the lumbar disc anteriorly.

In particular, the present invention provides a dynamic stabilization device positionable about a portion of a spinal column. The stabilization device generally includes a first component and a second component, where the first and second components are movably coupled to one another to define an arcuate path of motion therebetween which may be selectively adjusted for a particular application. The first component may include a body defining an opening providing access to a first cavity or recessed region, where the first cavity is able to receive an articulating portion of the second component.

The first and/or second components may further define one or more openings for the insertion or placement of an adjustment element that may be used to manipulate or otherwise modify the path of motion between the first and second components. The stabilization device may also include one or more adjustment elements positionable within first and second adjustment openings to affect the path of motion between the first and second components and/or the behavior and characteristics of the movement. In addition to the adjustment elements, one or more resistive elements may be adjustably positionable within either and/or both of the first and second adjustment openings to provide resistance and/or dampening of the forces experienced as the first and second components move relative to one another.

The stabilization device may further provide multiple degrees of freedom of movement to compensate for inaccuracies experienced during implantation and/or to allow the device to adapt to movements of a spinal segment. In addition, the stabilization device may also include one or more attachment elements for facilitating affixation of the device to the spinal segment.

The present invention further provides a spinal stabilization device positionable about a posterior side of a spinal segment, including a first component defining a cavity therein; a second component slidably positionable within the cavity of the first component; a first adjustment element movably positioned within the cavity to affect a range of motion between the first and second components; and a second adjustment element movably positioned within the cavity to affect the range of motion between the first and second components. The device may include a first actuating element movably coupled to an exterior surface of the first component, where the first actuating element is engaged to the first adjustment element for movement thereof, and a second actuating element movably coupled to an exterior surface of the first component, where the second actuating element is engaged to the second adjustment element for movement thereof.

One or more resistive elements may be coupled to the second component to resist movement thereof, and the resistive elements may include a conical spring positioned within the cavity of the first component.

• Provisional Patent
• Utility Patent

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